Engine manufacturers continue to seek improved fuel economy through engine design. Alternative approaches in improving fuel economy include formulating new fuels and engine oils. Combustion engines such as automobile engines typically require high octane gasoline for efficient operation. In the past, lead was added to gasoline to increase the octane number. Due to health and environmental concerns, however, lead was removed from gasoline. Lead can also poison a catalytic converter dramatically reducing its lifetime. Oxygenates, such as methyl-t-butyl ether (MTBE) and ethanol, may be added to gasoline to increase the octane number. While generally less toxic than lead, some suggest MTBE can be linked to ground water contamination. There is also a desire by some to reduce some of the high octane components normally present in gasoline, such as benzene, aromatics, and olefins.